Disable stretch in IK bones
I think that this rig is intended to let the user stretch the legs, so during animation process you can choose if to leave the foot close to the leg without stretching or move it away with stretch effect: note that bones do not stretch at all, only mesh does. If you want to constraint the foot to the leg, the foot deforming bone (which in this rig is reversed 180 degrees) should be parented and connected to the leg bone; the IK controller should be positioned at the end of the leg bone, but parented to the main character controller, so that moving the IK controller will move the leg chain, and the leg chain will move the foot, always connected. There are many ways of rigging a foot (which is the most difficult challenge in rigging human body): my favourite is this, which is pretty similar to the Rigify's one: https://www.youtube.com/watch?v=VVHKBSknFhA&amp;t=6s